Circuit for controlling arc energy from an electrosurgical generator

ABSTRACT

A circuit is disclosed which minimizes the amount of tissue vaporized during a first half (positive half cycle) of an electrosurgical current cycle and minimizes the amount of current applied to tissue during a second half (negative half cycle) of the electrosurgical current cycle to control thermal spread. The circuit is preferably provided within an electrosurgical generator which is capable of controlling the amount of energy delivered to a patient during electrosurgery on a per arc basis.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/728,212 filed on Dec. 4, 2003 by David S. Keppel entitled “CIRCUITFOR CONTROLLING ARC ENERGY FROM AN ELECTROSURGICAL GENERATOR,” now U.S.Pat. No. 7,044,948, which claims priority from U.S. ProvisionalApplication No. 60/432,384 filed on Dec. 10, 2002 by David S. Keppelentitled “CIRCUIT FOR CONTROLLING ARC ENERGY FROM AN ELECTROSURGICALGENERATOR,” the entire contents of which are hereby incorporated byreference herein.

BACKGROUND

1. Technical Field

The present disclosure is directed to electrosurgery and, in particular,to circuitry for controlling arc energy from an electrosurgicalgenerator for ablating, cauterizing, coagulating, cutting and/or sealingbody tissue during electrosurgery.

2. Description of the Related Art

Electrosurgical generators do not have the ability to vary the amount ofenergy contained within an arc to control the amount of tissue vaporizedand the amount of current applied to tissue to limit collateral damageto surrounding tissue, e.g., thermal spread. The ultimate amount of arcenergy from the electrosurgical generator to the tissue is dependent onpatient resistance, power setting and the internal impedance of theelectrosurgical generator.

Vaporization of tissue is proportional to the amount of energy in anarc. This energy in combination with the Cathode Fall Voltage, derivesthe power for vaporization. Thermal spread is dependent on the amountgenerated within the tissue is dependent on tissue resistive and the arcenergy squared. As can be appreciated, by not controlling the thermalspread the depth of ablation is difficult to predict and control.Electrosurgery is thus disadvantageous in applications in which only afine layer of tissue is to be ablated, or in areas of the body such asthe heart or near the spinal cord where resistive heating can result inundesirable collateral damage to critical tissue and/or organs.

U.S. Pat. No. 6,413,256 B 1 to Truckai et al. discloses anelectrosurgical system where a spark gap is utilized in series with theelectrosurgical generator output current to control resistive heating oftissue during electrosurgery. The spark gap limits the arc energy, butis prone to introducing high frequency oscillations that can have anundesirable effect on the tissue, as well as increase the high frequencyleakage currents.

Therefore, it is an aspect of the present disclosure to provide acircuit for controlling arc energy from the electrosurgical generator tominimize the amount of tissue vaporized and to also minimize the amountof current applied to tissue to limit thermal spread without introducinghigh frequency oscillations or other undesirable effects.

SUMMARY

A circuit is disclosed which minimizes the amount of tissue vaporizedduring a first half (positive half cycle) of an electrosurgical currentcycle and minimizes the amount of current applied to tissue during asecond half (negative half cycle) of the electrosurgical current cycleto limit thermal spread. The circuit is provided within anelectrosurgical generator to provide an electrosurgical generator whichis capable of controlling the amount of energy delivered to a patientduring electrosurgery on a per arc basis.

In a first embodiment, the circuit includes a diode-resistor blockhaving a pair of diodes in series with an output current of theelectrosurgical generator and tissue resistance. In a second embodiment,the diode-resistor block includes the pair of diodes in parallel withthe output current of the electrosurgical generator and the tissueresistance. In both embodiments, each diode is biased opposite from theother diode, thus splitting the output current into two paths. Thediode-resistor block in both embodiments includes two resistors whichare provided in each of the two paths. These resistors, depending ontheir resistive value, limit the current for each half cycle.

As long as the current for either half cycle remains above apredetermined minimum current, I_(min), an arc is formed. The energy inthe arc is limited by the resistors. Accordingly, the arc energy forvaporizing tissue during the positive half cycle and the arc energy forcausing thermal spread during the negative half cycle are controlled.

In alternate embodiments, the resistors of the diode-resistor block arereplaced with potentiometers for allowing a user of the electrosurgicalgenerator to “dial” in preferred levels of tissue vaporization andthermal spread. With these embodiments, the surgeon is given an almostunlimited ability to vary the ratio between the amount of tissuevaporized and thermal spread.

Further features of the above embodiments will become more readilyapparent to those skilled in the art from the following detaileddescription of the apparatus taken in conjunction with the drawings.

According to one aspect of the present disclosure a circuit forcontrolling arc energy from an electrosurgical generator is disclosed.The circuit includes a diode-resistor block configured in series with anoutput current generated by an electrosurgical generator. Thediode-resistor block is further configured to limit the amount of outputcurrent for at least one half cycle of the output current. Thediode-resistor block is connected in series with tissue.

According to another aspect of the present disclosure a circuit forcontrolling arc energy from an electrosurgical generator is disclosed.The circuit includes means for receiving an output current generated byan electrosurgical generator. The circuit also includes a diode-resistorblock electrically connected to the means for receiving the outputcurrent. The diode-resistor block is configured to limit the amount ofoutput current for at least one half cycle of the output current. Thediode-resistor block is connected in parallel with tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will be described herein below with reference to thedrawings wherein:

FIG. 1 is a schematic diagram of a circuit according to a firstembodiment;

FIG. 2 is a schematic diagram of a circuit according to a secondembodiment;

FIG. 3 is a schematic diagram of a circuit according to a thirdembodiment; and

FIG. 4 is a schematic diagram of a circuit according to a fourthembodiment.

DETAILED DESCRIPTION

Reference is made to the drawings where like reference numerals refer tosimilar elements. Referring to FIG. 1, there is shown a schematicdiagram of a circuit according to one embodiment of the presentdisclosure generally identified by reference numeral 100. Circuit 100includes a diode-resistor block 102 in series with an output current 104of an electrosurgical generator 106. The diode-resistor block 102includes a pair of diodes 108 a, 108 b biased opposite from each other,thus splitting the output current 104 into two paths 110 a, 110 b.Preferably, the diodes 108 a and 108 b are high voltage, fast recoveringdiodes.

The diode-resistor block 102 further includes resistors 112 a, 112 b ineach of these two paths 110 a, 110 b. These resistors 112 a, 112 b,depending on their resistive value (including having no resistive value,i.e., short), limit the current for each half cycle of the outputcurrent 104. Preferably, the resistance value for resistors 112 a and112 b is in the range of about 50 ohms to about 2000 ohms.

The output current 104 is further limited by the patient resistance 114in series with the diode-resistor block 102. The resistive value of theresistor 114 is typically in the range of 100 to 4000 ohms. By limitingthe current for the positive half cycle, the circuit 100 controls theamount of vaporization of the tissue. By limiting the current for thenegative half cycle, the circuit 100 controls thermal spread tosurrounding tissue. During the periods of reduced power, the thermalenergy is allowed to dissipate which reduces the overall thermalconduction and reduces the amount of steam exiting the surgical site. Adetailed explanation of this effect is disclosed in commonly-assignedU.S. Pat. No. 6,228,080, the entire contents of which are herebyincorporated by reference herein.

In circuit 100, the voltage can drop at two spots: across resistor 112 aand across patient 114 for maintaining arc at a predetermined minimumvoltage, V_(min), the minimum voltage point at which the arcdisappears). As can be appreciated, as long as the current for eitherhalf cycle remains above a predetermined minimum current, I_(min), anarc is formed. The energy in the arc is limited by the resistors 112 aand 112 b and patient resistance 114. Accordingly, the arc energy forvaporizing tissue during the positive half cycle and the arc energy forcausing thermal spread during the negative half cycle are controlled.

It is provided that according to the resistive values selected for theresistors 112 a and 112 b the output current 104 may be limited for onlyone of the half cycles.

In an alternate embodiment according to the present disclosure as shownby FIG. 3, a circuit 300 is provided which is similar to circuit 100.However, in this embodiment, the resistors 112 a, 112 b are replacedwith potentiometers 312 a, 312 b for allowing a surgeon to select theresistive value (including no resistive value, i.e., short) forpotentiometers 312 a, 312 b using dials 320 a, 320 b, respectively, onthe electrosurgical generator 106 for varying the ratio between theamount of tissue vaporized during the positive half cycle and thermalspread during the negative half cycle. In circuit 300, the voltage candrop at two spots: across potentiometer 312 a and across the patient 114for maintaining arc at a predetermined minimum voltage, V_(min).

It is envisioned that by selecting the resistive values for thepotentiometers 312 a and 312 b, the output current 104 may be limitedfor only one of the half cycles.

Referring to FIG. 2, there is shown a schematic diagram of a circuit 200according to another embodiment of the present disclosure. Circuit 200includes a diode-resistor block 202 in parallel with the output current204 of an electrosurgical generator 206. The diode-resistor block 202includes a pair of diodes 208 a, 208 b biased opposite from each other,thus splitting the output current 204 into two paths 210 a, 210 b. Thediode-resistor block 202 shunts the current around the patient 214. Thisforms two paths; the path through the diode circuit block 202 and thepath through the patient 214.

The diode-resistor block 202 further includes resistors 212 a, 212 b ineach of these two paths 210 a, 210 b, respectively. These resistors 212a, 212 b, depending on their resistive value (including having noresistive value, i.e., short), shunt the current for each half cycle ofthe output current 204.

The output current 204 is further limited by the patient resistance 214in parallel with the diode-resistor block 202. The resistive value ofthe patient 214 is typically in the range of 100 to 4000 ohms. Byshunting the current for the positive half cycle, the circuit 200controls the amount of vaporization of the tissue. By shunting thecurrent for the negative half cycle, the circuit 200 controls thermalspread to surrounding tissue. In circuit 200, the predetermined minimumvoltage, V_(min), is controlled within the generator 106 and, thus, thevoltage does not drop across the patient 214 to maintain or controlV_(min).

In short, as long as the current for either half cycle remains above apredetermined minimum current, I_(min), an arc is formed. The energy inthe arc is shunted by the resistors 212 a and 212 b. Accordingly, thearc energy for vaporizing tissue during the positive half cycle and thearc energy for causing thermal spread during the negative half cycle areadequately controlled. Moreover and depending upon the resistive valuesselected for the resistors 212 a and 212 b the output current 204 may belimited for only one of the half cycles.

In an alternate embodiment, as shown by FIG. 4, a circuit 400 isprovided which is similar to circuit 200. However, in this embodiment,the resistors 212 a, 212 b are replaced with potentiometers 412 a, 412 bfor allowing a surgeon to select the resistive value (including noresistive value, i.e., short) for potentiometers 412 a, 412 b usingdials 420 a, 420 b, respectively, on the electrosurgical generator 106for varying the ratio between the amount of tissue vaporized during thepositive half cycle and thermal spread during the negative half cycle.Much like circuit 200 described above, in 400 the predetermined minimumvoltage, V_(min), is controlled within the generator 106 and thus, thevoltage does not drop across the patient 214 to maintain or controlV_(min). The output current 104 may be shunted for only one of the halfcycles by selecting the values for the potentiometers 412 a and 412 b.

Accordingly, the present disclosure provides an electrosurgicalgenerator which is capable of controlling the amount of energy deliveredto a patient during electrosurgery on a per arc basis. As can beappreciated, controlling the power reduces the overall effect on thetissue and the surrounding tissue.

Although the present disclosure has been described with respect topreferred embodiments, it will be readily apparent to those havingordinary skill in the art to which it appertains that changes andmodifications may be made thereto without departing from the spirit orscope of the disclosure.

1. A circuit for controlling arc energy from an electrosurgicalgenerator, said circuit comprising: a diode-resistor block configured inseries with an output current generated by an electrosurgical generator,said diode-resistor block configured to limit the amount of outputcurrent for at least one half cycle of the output current wherein saiddiode-resistor block is connected in series with tissue and includes apair of diodes biased opposite from each other for splitting the outputcurrent into two paths, wherein each of the two paths includes one of aresistor and a potentiometer in series with a respective diode of thepair of diodes.
 2. A circuit according to claim 1, wherein saiddiode-resistor block is connected in parallel with said output currentgenerated by the electrosurgical generator.
 3. A circuit for controllingarc energy from an electrosurgical generator, said circuit comprising:means for receiving an output current generated by an electrosurgicalgenerator; a diode-resistor block electrically connected to said meansfor receiving the output current, said diode-resistor block configuredto limit the amount of output current for at least one half cycle of theoutput current, wherein said diode-resistor block is connected inparallel with tissue and includes a pair of diodes biased opposite fromeach other for splitting the output current into two paths, wherein eachof the two paths includes one of a resistor and a potentiometer inseries with a respective diode of the pair of diodes.
 4. A currentaccording to claim 3, wherein said diode-resistor block is connected inseries to said means for receiving the output current.
 5. A circuitaccording to claim 3, wherein said diode-resistor block is connected inparallel with said means for receiving the output current.